To provide an electric power steering device having simple structure and excellent easiness of assembly.

A cover 101B is formed by bending plate material and is deformed so as to expand when fitted into inner circumference of a body 101A. In this way, the cover 101B can be attached to the body 101A only by press-fitting without using any bolt, thereby reducing the cost of the cover 101B made by press-forming of the plate material compared to a conventional die casting forming, also effectively reducing working hours, and cutting down the weight and cost of the cover 101B. In addition, compared to a conventional structure in which backlash of a shaft is controlled by fixing an expensive four-point contact type ball bearing or the like to a steering shaft with a retaining ring, backlash of an output shaft 113 can be controlled only by using cheap deep groove ball bearings 114, 115 because the bearings can be biased by expanding force of the cover 101B.